Method for treating sulfides in waste streams

ABSTRACT

A method for treating sulfide in an aqueous fluid comprises contacting the fluid with an oxidizer in the presence of a sulfur dye or sulfurized vat dye. In one embodiment. the method comprises treating; sulfide contaminated water by contacting the contaminated water with a gas including oxygen in the presence of a sulfur dye or a sulfurized vat dye. The method is useful for remediating industrial, agricultural, and municipal wastewater.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 16/165,010 filed on Oct. 19, 2018, now U.S. Pat. No.10,315,940, which is a divisional application claiming priority to U.S.patent application Ser. No. 14/854,403 filed on Sep. 15, 2015, now U.S.Pat. No. 10,112,853, all of which are hereby incorporated by referenceherein in their entirety. This application is also co-pending with U.S.patent application Ser. No. 16/397,123, filed on Apr. 29, 2019, which isa continuation application claiming priority to U.S. patent applicationSer. No. 16/165,010.

FIELD OF THE INVENTION

The present invention relates to the treatment of aqueous solutionscomprising sulfides. More particularly, the present invention is aprocess for the treatment of sulfides in an aqueous solution wherein theaqueous solution comprising the sulfides is contacted with a sulfur dye.The present invention is useful for the remediation of sulfides found innatural and industrial aqueous waste streams, wastewater or absorptionliquids derived from the absorption of hydrogen sulfide contained ingases. More particularly, the wastewater comprising sulfides can resultfrom industrial operations such as animal waste processing, mining, orerefining, oil drilling, petroleum refining, natural gas processing, andhydraulic fracturing.

BACKGROUND

Current methods of raising commercial livestock include housing a largenumber of animals within a confined space. Numerous drawbacks of suchconfinement include, but are not limited to, the significant amount ofwaste which must be removed periodically to ensure adequate sanitationand to prevent disease and the hydrogen sulfide in the ambient airwithin the animal enclosure.

The most common commercial waste removal method is to flood the housingarea with water to wash away the waste comprising urine and manure. Theresulting waste, that being a liquid/solid manure slurry, can bedirected to a tank, or more commonly a manmade surface impoundment orlagoon, where the solids and particulates settle to the bottom and thewaste decomposes predominantly under anaerobic conditions

Anaerobic organisms can degrade many waste constituents without theadded expense of mechanical aeration and complete mixing. This type oftreatment commonly produces methane gas and sulfides, particularlyhydrogen sulfide. Hydrogen sulfide emitting from uncovered anaerobictreatment systems will create foul odors and can also be a safety hazardin confined areas. The methane gas generated could be captured as a fuelif the treatment unit is covered, but the gas is normally stillcontaminated with hydrogen sulfide which must be reduced to acceptablelevels if the methane is to be used for energy generation.

Numerous industrial processes generate hydrogen sulfide which can becaptured by absorbers/scrubbers to produce non-volatile compounds suchas sodium bisulfide. Crude natural gas and biogas frequently containhydrogen sulfide as a contaminant which can be removed by absorption.Hydrogen sulfide can also be an ambient air pollutant which can bepresent in industrial settings and in environments where anaerobicdegradation of organic compounds is occurring, such as concentratedanimal feeding buildings and pits.

Absorption liquids containing sulfides are generated when a gascontaining hydrogen sulfide is processed in an absorber or scrubberwhere it contacts an aqueous liquid to absorb the hydrogen sulfide.While hydrogen sulfide has some solubility in water, the amount of gasdissolved is limited. Typically, the aqueous liquid will contain analkali to convert the hydrogen sulfide into a water-soluble bisulfide orsulfide ion to greatly enhance the rate and amount of hydrogen sulfidethat is absorbed into the liquid. The base can be added as a singlecharge or can be added throughout the absorption as alkalinity isconsumed by the hydrogen sulfide. In some instances, gases other thanhydrogen sulfide may be in the gas stream to be absorbed. If the gashappens to be an alkaline gas, such as ammonia, the amount of base added(if any) to the absorption liquid can be reduced.

One method of eliminating sulfides is to oxidize them to a new compoundthat is not malodorous or toxic. The oxidation of sulfides in aqueousliquids can be accomplished chemically with oxidizing agents such ashydrogen peroxide, chlorine dioxide, hypochlorite salts,methylmorpholine-N-oxide, nitrate /nitrites. These methods are effectivebut have drawbacks which can include high chemical costs, handling ofhazardous chemicals and formation of unwanted by-products. Oxidation canbe accomplished biologically, but this is usually expensive and canproduce odors in the treatment units. A third method is oxidation withmolecular oxygen in the presence of a catalyst. Sulfides may also betreated by other methods such as absorption or sequestering.

The most common catalyst for sulfide oxidation is a chelated metalcatalyst, most particularly iron chelated by an aminopolycarboxylicacid. The normal product of oxidation with this catalyst in aqueousfluids is elemental sulfur which precipitates. The catalyst is typicallyregenerated with molecular oxygen, normally atmospheric air which canalso degrade the catalyst. This method for oxidizing sulfides is notwithout drawbacks. It requires removal of solid elemental sulfur andreplenishment of catalyst.

There is a continued need for a simple and efficient method of removingsulfides from a waste stream, for example, from wastewaters comprisingbiologically degradable constituents that produce sulfides. There isalso a need for a process to reduce the level of hydrogen sulfide inambient air within animal enclosures without generating a hazardousbyproduct.

BRIEF SUMMARY OF THE INVENTION

The present invention provides an inexpensive alternative to thetraditional treatment of sulfides by expensive chemicals or by oxygencatalyzed by chelated metal which creates a sulfur precipitate. It hasbeen discovered that sulfur dyes and sulfurized vat dyes will oxidizesulfides dissolved in aqueous fluids when the fluid is contacted with agas comprising oxygen, for example, atmospheric air. The presentinvention uses small amounts of inexpensive dye as a means for oxidationof sulfides in the presence of oxygen or other oxidizers. Sulfur dyesand sulfurized vat dyes are stable under the highly alkaline conditionsoften associated with absorption or scrubbing of hydrogen sulfide fromgaseous streams. Sulfide oxidation under alkaline conditions in thepresence of sulfur dye is very simple and predominantly produces anon-toxic soluble by-product, thiosulfate. In many applications, thesoluble nature of the treatment product will be an advantage.

In one embodiment, the present invention is a method for treatingsulfide in an aqueous fluid comprising contacting the fluid with anoxidizer in the presence of at least one sulfur dye or sulfurized vatdye.

In a further embodiment, the present invention is a method for treatingsulfides present in wastewater, wherein the sulfides are present in thewastewater as a result of the anaerobic degradation of biologicallydegradable constituents by bacteria. The method comprises contacting thewastewater comprising the sulfides with an oxidizer in the presence ofat least one sulfur dye or sulfurized vat dye.

In a still further embodiment, the present invention is a method fortreating sulfide produced by hydrogen sulfide absorption in an alkalineaqueous liquid to form an adsorption liquid comprising dissolvedsulfides. The method comprises contacting the absorption liquid with atleast one sulfur dye or sulfurized vat dye and concurrently orsubsequently contacting the absorption liquid with an oxidizer toprovide a treated liquid.

In still a further embodiment, the present invention is a method forcollecting and treating hydrogen sulfide present as a pollutant inambient air, by absorbing (or scrubbing) the hydrogen sulfide out of theambient air into an aqueous liquid having a pH maintained at about 7 orabove in the presence of at least one sulfur dye or a sulfurized vat dyeto oxidize the absorbed sulfides using oxygen present in the ambientair. The products of the oxidation are non-hazardous water solubleconstituents, predominately thiosulfate.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a method of treating water comprisingsulfides, for example, wastewaters comprising biologically degradableconstituents which generate sulfides during anaerobic degradation.

As defined herein, the term sulfide includes all forms of inorganicsulfide including hydrogen sulfide, bisulfide ions, sulfide ions andpolysulfide ions.

As defined herein, “biologically degradable constituents” includes wastefrom animals such as humans, dairy cattle, beef cattle, swine, poultry,horses, rabbits, and other concentrated animal raising operations.Animal waste can comprise a mixture of feces and urine as well as wastedfeed, bedding and water. Waste characteristics are generally affected bydiet, species and the growth stage of the animals, and the wastecollection method used, including the amount of water added to dilutethe waste. Typically, animal waste is about 80% to about 95% liquid byweight due to urine, sloppy drinking, animal washing and flush water. Assuch, the animal waste may be pretreated with mechanical systems toremove any unwanted material, larger solids and excess liquids from theanimal waste before treatment using the process described herein,wherein the pretreating includes systems comprising at least one of ascrew press, a centrifuge, a vibrating screen, mesh screening, a beltfilter, a hydrocyclone and other systems that may further reduceparticle size and/or remove unwanted large material to ensure easyprocessing using the method described herein.

The biologically degradable constituents may be treated in an anaerobictreatment unit, which includes holding the biologically degradableconstituents in an air-tight tank or a covered surface impoundment.Bacteria will degrade the biologically degradable constituents in theseconditions, generating a number of products including, but not limitedto, sulfides and methane gas. The methane can be harvested andburned/combusted for energy production. Advantageously, anaerobictreatment does not reduce the nutrients in the biologically degradableconstituents, although it may alter the form of the nitrogen (moreammonia) and phosphorus (more orthophosphate). Accordingly, thebiologically degradable constituents can be further processed to produceadditional products such as fertilizer. Disadvantageously, the sulfidesneed to be separated from the methane gas to maximize the potentialenergy of the methane.

The biologically degradable constituents may also be treated in afacultative anaerobic treatment unit in which there are both anaerobicand aerobic treatment zones. This type of treatment occurs typically inopen surface impoundments and tanks when there is insufficient mixingand/or oxygen input to result in completely aerobic treatmentconditions. Hydrogen sulfide and methane will commonly be produced inthe anaerobic zone. While a portion of the sulfide may be oxidized inthe aerobic zone, most facultative units will not eliminate all thehydrogen sulfide and will emit a significant portion to the atmosphere.

Selectively treating sulfides as part of the wastewater treatmentprocess using sulfur dyes or sulfurized vat dyes as a catalyst in thepresence of oxygen will reduce or eliminate problems posed by elevatedsulfide levels. The amount of oxygen needed will be very small comparedto that needed for aerobic treatment. The dye-catalyzed oxidation can beemployed in both covered and uncovered treatment units, although thebenefits will be greater in covered units designed to capturebiologically generated methane. Where methane is present, care needs tobe taken to avoid an explosive mixture of methane and oxygen.

In one aspect, a method of removing sulfides from wastewater comprisesremoving the wastewater from an anaerobic or facultative treatment unitto a treatment container, wherein the wastewater comprises sulfides,adding at least one sulfur dye or sulfurized vat dye catalyst to thewastewater to form a mixture, aerating the mixture with a gas comprisingoxygen to oxidize the sulfides to yield treated water, and returning thetreated water to the anaerobic/facultative treatment unit. The returnedtreated water will contain both dissolved oxygen and the oxidized formof the catalyst; both of which will provide additional oxidation ofsulfides within the surface impoundment. The anaerobic treatment unitincludes, but is not limited to, an air-tight tank or a covered surfaceimpoundment. The facultative treatment unit comprises at least oneanaerobic zone. The at least one sulfur dye or sulfurized vat dyecatalyst can optionally be removed from the treated water by filtration,ultrafiltration, or other means of separation prior to reintroduction ofthe treated water into the anaerobic or facultative treatment unit.Maintaining the mixture at a pH of neutral or above (i.e., pH greaterthan or equal to 7, preferably in a range from about 7 to about 11)while in the treatment container will provide the added benefit ofconverting the sulfides to a water soluble product, includingthiosulfate, and avoiding the precipitation of elemental sulfur. Tomaintain the pH at greater than or equal to 7, at least one base can beadded, wherein said at least one base can comprise a species selectedfrom the group consisting of sodium hydroxide, potassium hydroxide,ammonia, ammonium hydroxide, calcium hydroxide, magnesium hydroxide, andany combination thereof The pH can be monitored and adjustedcontinuously or periodically, as readily understood by the personskilled in the art. The at least one base can be chosen to enhance thedownstream fertilizer value of the treated wastewater. The sulfides maybe present in the wastewater as a result of the degradation of thebiologically degradable constituents by bacteria during anaerobicdigestion. With the removal of the sulfides from the wastewater, theother product of the anaerobic digestion, i.e., methane, can beharvested for energy production with a significantly reduced hydrogensulfide content. The at least one sulfur dye or sulfurized vat dyecatalyst separated in this manner can be reused in the sulfide oxidationprocess.

It should be understood that the gas comprising oxygen can be air, pureoxygen, or a gas comprising oxygen in some percentage between about 10%and about 100%, by volume. In an uncovered unit, the source of oxygencan come solely from the surface transfer of oxygen from the air fortreatment.

An oxidation/reduction potential (ORP) meter can be used to determinewhen the sulfides have been substantially treated prior toreintroduction into the anaerobic or facultative treatment unit. In mostmatrices, an ORP reading will become less negative as sulfide isoxidized. Depending on the matrix, a reading less negative than about−100 mV usually indicates that the sulfides have been substantiallytreated.

The anaerobic or facultative treatment container can be a coveredcontainer or an uncovered container, as readily determined by the personskilled in the art. The mixture in the treatment container can beagitated, for example by stirring, sonication, aeration, shaking, or anycombination thereof.

The method can be operated over a wide range of conditions, includingtemperature, sulfide concentration, dye concentration, and oxygen input.The rate of sulfide treatment is dependent, at least to some extent, onall four of these parameters. While a higher temperature will generallyincrease the reaction rate, a higher temperature will also tend toreduce the solubility of oxygen in water. Solubility of oxygen in wateris increased by higher pressure. The optimum conditions for best economydepend greatly on the particular circumstances. Since the presentinvention has utility in a vast range of applications, the optimumconditions will vary widely also. The examples provided demonstrate therobust nature of this method over a wide range of conditions.

The process may be utilized in numerous wastewater treatmentapplications. Addition of sulfur dye and introduction of oxygen tovirtually any sulfide bearing aqueous solution will reduce the sulfideconcentrations. Sulfide treatment systems can be set up to operatecontinuously or as batch processes. The method will have applications inoil field operations to reduce sulfide in waters associated with oil andgas production. In one embodiment, the sulfur dye is retained byfiltration, ultrafiltration, or other means of separation to allow thetreated water and soluble salts to be reused in the oilfield operation.The method of this invention may also be used in downhole treatment ofsulfide bearing waters in oilfields.

In a very simple application, small amounts of sulfur dye added towastewater impoundments can provide very economical sulfide treatmentwhere oxygen input is accomplished by surface transfer of atmosphericoxygen.

In one embodiment, the method can be incorporated into the absorptionprocess for removing hydrogen sulfide from gaseous streams. Sulfur dyecan be added directly to an aqueous absorption liquid having a pHgreater than 7, preferably in a range from about 7 to about 11, where anoxidizer, typically comprising or containing oxygen or air, is added tothe system. Preferably, the absorption liquid is sufficiently alkaline(having a pH greater than 9) to facilitate the absorption of hydrogensulfide. Molecular oxygen, typically atmospheric air, can be added atany convenient place in the absorption system provided safety concernsof mixing oxygen with concentrated methane and hydrogen sulfide gasesare considered. A treatment unit may be operated at greater thanatmospheric pressure to facilitate the dissolving or contacting of theoxygen in the aqueous absorption liquid. Under the alkaline conditionsemployed to absorb hydrogen sulfide into an aqueous liquid, it isbelieved that the primary products of the treatment with the sulfur dyeare thiosulfates. The form of the thiosulfates depends on which alkali(such as: sodium hydroxide, potassium hydroxide, ammonium hydroxide,calcium hydroxide, or magnesium hydroxide) is used in the absorptionliquid. Optionally, filtration, ultrafiltration or other means ofseparation can be used to separate the soluble products of the sulfidetreatment from any insoluble sulfur dye that is retained by theseparator. Sulfur dye compounds separated in this manner can be reusedin the sulfide oxidation process. Caution is required when a highconcentration of flammable hydrogen sulfide and/or other flammable gasare involved to avoid an unsafe condition of an explosive atmosphere.For example, the gas from the anaerobic unit e.g., above the liquid, isdirected to an absorption unit, wherein the absorption unit comprises anaqueous absorption liquid comprising the at least one sulfur dye orsulfurized vat dye catalyst, wherein the aqueous absorption liquid has apH greater than 7, preferably in a range from about 7 to about 11, toform a reaction mixture. A gas comprising oxygen is introduced to thereaction mixture to oxidize the sulfide. Preferably, the aqueousabsorption liquid is sufficiently alkaline (having a pH greater than 9)to facilitate the absorption of sulfide therein.

In another embodiment, hydrogen sulfide occurring as a pollutant inambient air can be collected and treated in a combined process byabsorbing the hydrogen sulfide into an aqueous absorption liquidcomprising at least one sulfur dye or sulfurized vat dye. The absorptionliquid should be maintained at a pH of about 7 or above using any of anumber of bases, chosen predominantly for low cost, ease of use andfertilizer value. Bases comprising carbonates, which can produce a gaswhen acidified, are not recommended because they may interfere with theabsorption process. A pH higher than 7 will enhance the absorption ofthe hydrogen sulfide. In some instances, the ambient air may alsocontain an alkaline gas, such as ammonia, which will be absorbed in theaqueous absorption liquid and reduce the amount of base required. Thepresence of oxygen in the ambient air will allow the oxidation of theabsorbed sulfide to occur concurrently with the absorption process. Theproducts of the oxidation are non-hazardous water-soluble constituents,predominately thiosulfate. Typically, the absorption fluid will berecycled through the absorption unit numerous times.

The sulfur dyes and sulfurized vat dyes which may be used in accordancewith the processes of the invention include those which are either 1)provided in the non-reduced (oxidized) form (where sulfur atoms attachedto the dye chromophore are predominantly connected to other chromophoreunits through disulfide or polysulfide linkages), 2) provided aspre-reduced (Leuco) sulfur dyes (where sulfur atoms exist primarily asthiolate salts), or 3) provided as solubilized sulfur dyes where Buntesalt groups impart water solubility under non-reducing conditions.

Sulfurized vat dyes are chemically and structurally similar to sulfurdyes including having the disulfide/thiolate functionality. They aregiven the vat dye designation because they are typically dyed using avat dye process.

Sulfur dyes and sulfurized vat dyes can be dissolved by reducing agentssuch as sodium sulfide, sodium dithionite or sodium hydrosulfide underalkaline conditions. This reduction breaks the disulfide bonds producingvery polar thiolate groups (Dye-S⁻). This form of the dye is called aLeuco Sulfur Dye. The oxidation/reduction of the sulfur atoms attachedto the chromophore structure is reversible as follows:

2 Dye-S⁻+oxidizer→Dye-S-S-Dye+reducing agent→2Dye-S⁻

Sulfur dyes can also exist as a non-reduced, water soluble formcharacterized by thiosulfate groups attached to the chromophores(Dye-S-SO₃ ⁻). This form is called a Bunte Salt and is categorized as aSolubilized Sulfur Dye. Solubilized Sulfur Dyes can be prepared byoxidative reaction of a sulfur dye with sulfite. Solubilized Sulfur Dyeswill convert to one of the other dye forms when reacted with sulfides.Any of the three forms of sulfur dyes may be used in accordance withthis method.

During sulfur dye production and dyeing processes, sulfides can undergooxidation when Leuco dyes are converted to the insoluble non-reduced(oxidized) form with air. However, this oxidation of sulfides has notbeen attributed to the presence of the dye. There is no evidence thatanyone has recognized that the addition of sulfur dyes or sulfurized vatdyes will act as a catalyst for the treatment of unwanted sulfides inwaste waters and other aqueous fluids. It has been discovered that thesedyes, even in very low molar concentrations, will treat sulfides inaqueous fluids.

Without being bound by theory, it is believed that the mechanism of thesulfide treatment of the present invention is that the sulfur dye in thenon-reduced (oxidized) form reacts with sulfide in solution to oxidizethe sulfide to a harmless compound, such as sodium thiosulfate. Inreacting the sulfur dye in the sulfide treatment process, the sulfur dyeis converted to the Leuco (reduced) form of the dye. When the thusproduced Leuco form of the dye is contacted with oxygen or anothersuitable oxidizer, the Leuco dye is restored to the non-reduced stateready to react with more sulfide. If the absorption liquid is contactedwith a Leuco form of the sulfur dye; it is required to simultaneouslycontact the absorption liquid with an oxidizer such as air to providethe sulfide treatment. While the exact structures and molecular weightsof most sulfur dyes are not known, the molecular weight of an individualchromophore unit of Sulfur Black 1 is believed to be about 548 based ona common proposed structure. This molecular weight is about 14 times theweight of a sulfide ion. The method of this invention is demonstrated tobe very effective at molar ratios of sulfur dye to sulfide that are lessthan 1 mole %. More preferably, the molar ratio of sulfur dye to sulfideis effective at less than about 0.6 mole %. This strongly supports thatthe dye used in this method acts as a catalyst to provide the sulfidetreatment.

Sulfur dyes and sulfurized vat dyes which may be utilized in accordancewith the method of the invention include but are not limited to thefollowing (“C.I.” stands for “Colour Index”):

-   C.I. Sulfur Yellow 1, 2, 3, 4, 5, 6, 8, 9, 10, 11, 12, 13, 14, 16,    20 and 23, C.I. Leuco Sulfur Yellow 2, 4, 7, 9, 12, 15, 17, 18, 21,    22 and 23 and C.I. Solubilized Sulfur Yellow 2, 4, 5, 19, 20 and 23;-   C.I. Sulfur Orange 1, 2, 3, 4, 5, 6, 7 and 8, C.I. Leuco Sulfur    Orange 1, 3, 5 and 9 and C.I. Solubilized Sulfur Orange 1, 3, 5, 6,    7 and 8;-   C.I. Sulfur Red 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12 and 13, C.I. Leuco    Sulfur Red 1, 4, 5, 6, 11 and 14 and C.I. Solubilized Sulfur Red 3,    6, 7, 11 and 13;-   C.I. Sulfur Violet 1, 2, 3, 4 and 5, C.I. Leuco Sulfur Violet 1 and    3 and C.I. Solubilized Sulfur Violet 1;-   C.I. Sulfur Blue 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15,    16, 17, 18 and 19, C.I. Leuco Sulfur Blue 1, 2, 3, 5, 7, 8, 9, 11,    13, 15 and 20 and C.I. Solubilized Sulfur Blue 1, 2, 4, 5, 6, 7, 10,    11, 13, and 15;-   C.I. Sulfur Green 1, 2, 3, 4, 5, 6, 7, 8:1, 9, 10, 11, 12, 13, 14,    15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 31, 32    and 33, C.I. Leuco Sulfur Green 1, 2, 3, 4, 7, 11, 16 30, 34, 35,    36, and 37 and C.I. Solubilized Sulfur Green 1, 2, 3, 6, 7, 9, 19,    26, and 27;-   C.I. Sulfur Brown 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,    14:1, 15, 15:1, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28,    29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45,    46, 47, 48, 49, 50, 51, 52, 53, 53:1, 54, 55, 56, 57, 58, 59, 60,    61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 76, 77, 78,    79, 84, 85, 87, 88, 89, 90, 91, 93, and 94;-   C.I. Leuco Sulfur Brown 1, 3, 4, 5, 8, 10, 11, 12, 14, 15, 21, 23,    26, 31, 37, 43, 44, 81, 82, 86, 87, 90, 91, 92, 93, 94, 95 and 96    and C.I. Solubilized Sulfur Brown 1, 4, 5, 8, 10, 11, 12, 14, 15,    16, 21, 26, 28, 31, 51, 52, 56, 60, 75, 80, and 83;-   C.I. Sulfur Black 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15,    16 and 17;-   C.I. Leuco Sulfur Black 1, 2, 6, 9, 10, 11, and 18;-   C.I. Solubilized Sulfur Black 1, 2, 5, 7, and 11; and,-   C.I. Vat Yellow 21, C.I. Vat Orange 21, C.I Vat Green 7, C.I. Vat    Blue 7, 42, 43, Vat Black 11.

A more complete listing of the sulfur dyes and sulfurized vat dyesmentioned hereinabove may be found in the Colour Index, 3rd. Ed., issuedby the Society of Dyers and Colourists (London, GB), as well as in thesupplementary volumes published thereto and in the Colour IndexInternational, 4^(th) Edition Online which are hereby incorporated byreference.

At least one sulfur dye or sulfurized vat dye listed hereinabove is usedto treat aqueous sulfides in the process of the instant invention. Morepreferably, at least one of C.I. Sulfur Black 1, C.I. Leuco Sulfur Black1 and C.I. Solubilized Sulfur Black 1 is utilized in accordance with theprocess to treat sulfides based on economics and availability.

Compounds other than those listed by Colour Index International mayexist or be synthesized which chemically qualify as sulfur dyes orsulfurized vat dyes and may be utilized in accordance with the method ofthis invention. Such compounds might not possess a sufficientlydesirable color or fastness to be offered as a dye, yet performacceptably in the method of this invention. The terms “sulfur dye” and“sulfurized vat dye” as used in this invention include compoundscomprised of monocyclic aromatic, heteroaromatic, or quinoid chromophoreunits; or polycyclic aromatic, heteroaromatic, or quinoid chromophorewherein said chromophore units are connected by disulfide or polysulfidelinkages when in the non-reduced form. Sulfur dyes and sulfurized vatdyes can be converted to the reduced (or Leuco) form by reaction withreducing agents such sodium sulfide, sodium dithionite or sodiumhydrosulfide. This reaction cleaves the disulfide linkages of thenon-reduced (oxidized) dye to form thiolate functional groups (dye-S⁻).This conversion between disulfide and thiolate functionality isreversible.

A series of examples was developed and carried out to explore theconcept of the method for treating aqueous solutions containing sulfidesby contacting the aqueous solution containing the sulfide with a sulfurdye or sulfurized vat dye. It was discovered that the concentration ofsulfide in the aqueous sulfide solutions could be reduced by more than90 percent on the basis of the weight of the sulfide present in theaqueous sulfide solution. More preferably, the concentration of sulfidein the aqueous sulfide solutions could be reduced by more than 95percent on the basis of the weight of the sulfide present in the aqueoussulfide solution. Most preferably, the concentration of sulfide in theaqueous sulfide solutions could be reduced by more than 96, 97, 98, 99,or 99.5 percent on the basis of the weight of the sulfide present in theaqueous sulfide solution. The process of the present invention wasdemonstrated over a reaction temperature range of from about 1° C. toabout 100° C. More preferably, the process of the present invention canbe carried out over a reaction temperature of from about 4° C. to about80° C. Most preferably, the process of the present invention can becarried out over a reaction temperature of from about 20° C. to about50° C. The sulfur dye was dissolved in aqueous sulfide solutions insulfur dye concentrations ranging from about 10 to about 1200 mg/l.These dye concentrations are based on the concentration of commercialdye products which contain less than 100% active dye ingredient. Overthe entire range of aqueous sulfide solutions having a concentration ofsulfide from about 100 to about 5000 mg/l, it was found that theaddition of sulfur dye or sulfurized vat dye resulted in a greater than96 weight percent reduction of the sulfide in the aqueous sulfidesolutions within a treatment time ranging from about 30 minutes to about120 minutes. When using Sulfur Black 1 as the sulfur dye, the reductionof the sulfide concentration ranged from about 97 to about 99.6 weightpercent based on the initial amount of sulfide in the aqueous sulfidesolution to be treated, reducing the final concentration of sulfide fromas high as about 5000 mg/l to as low as less than about 1 mg/l sulfidein the treated effluent. Table 1 shows a summary of the results ofexperiments related to the reduction of sulfides in aqueous solutionsusing sulfur dyes and sulfurized vat dyes compared to a reference case(Zero) wherein no sulfur dye or sulfurized vat dye was added to theaqueous sulfide solution.

TABLE 1 Comparison of Sulfide Treatment with Sulfur Dyes and SulfurizedVat Dyes Dye Sulfide Sulfide Treatment Ex. Conc. Temp Initial Final TimeReduction No. Dye (mg/l) (° C.) (mg/l) (mg/l) (Min) (%) Zero None 043-46 500 >490 120 <2 1 Sulfur Black 1 251 43-46 478 <1 50 99.6 2 SulfurBlack 1 250 4-6 250 <5 120 >98 3 Sulfur Black 1 250 78-80 250 <130 >99.6 4 Sulfur Black 1 10 42-45 100 3 30 97 5 Sulfur Black 1 (reused)247.5 50 495 6 105 98.8 6 Leuco Sulfur Brown 37 1200 45-48 500 <2060 >96 7 Leuco Vat Blue 43 1200 44-45 500 <2.5 60 >99.5 8 Sulfur Black 1500 40-45 5000 50 75 99

EXAMPLES

The following examples are intended to demonstrate the wide range ofconditions under which sulfur dyes and sulfurized vat dyes are effectivein treating sulfide when an oxidizer (in these examples air) isintroduced into the aqueous fluid which contains the sulfide.

Example Zero Control Without Dye

A 1000 mg/l stock sulfide solution (as S⁻²) was made by dissolving 1.503grams of sodium sulfide nonahydrate in distilled water and diluting itto 250 milliliters. A 100 milliliter sample of 500 mg/l sulfide testsolution was made by diluting 50 milliliters of the stock solution to100 milliliters with distilled water. An aliquot was taken from thesulfide test solution for analysis under buffered pH and ionic strengthconditions using a sulfide specific ion electrode calibrated usingfreshly prepared sulfide standards. (This method of analysis was usedfor all sulfide analyses in the examples.) The test solution was stirredand heated to 45° C., at which time an air sparge through a diffuser wasinitiated. The stirred and aerated test solution was maintained at atemperature of 45+/−2° C. Samples were withdrawn for analysis every 30minutes for 2 hours. A decrease in sulfide concentration of less than 2%relative to the initial sulfide concentration of 500 mg/l was observedafter two hours, demonstrating that the sulfide concentration was notmarkedly affected by the test conditions.

Example 1 C.I Sulfur Black 1

While the initial test of Example Zero was underway, a 1% solution ofC.I. Sulfur Black 1 product was prepared by diluting 1 gram of C.I.Sulfur Black 1 to 100 milliliters with distilled water while stirringand heating to 80° C. A 1.8 milliliter portion of the 1% solution wasadded to the remaining 70 milliliters of test solution from Example Zeroto produce a calculated sulfide concentration of 478 mg/l and a SulfurBlack 1 product concentration of 251 mg/l. The test solution wasmaintained at the same test conditions of temperature, stirring and airsparging as the control in Example Zero. After 30 minutes of sparging,the sulfide concentration in the test sample of Example 1 had decreasedto less than 10 mg/l. After 50 minutes the sulfide concentration in thetest sample of Example 1 had dropped to less than 2 mg/l; a reduction ofapproximately 99.6% relative to the initial sulfide concentration of 478mg/l.

Example 2 C.I. Sulfur Black 1

A test solution containing 250 mg/l sulfide and 250 mg/l of C.I. SulfurBlack 1 product was made by diluting 25 milliliters of the 1000 mg/lsulfide stock solution prepared in Example Zero with 72.5 milliliters ofdistilled water. The test solution of Example 2 was cooled to 5° C., andthen 2.5 milliliters of the 1% Sulfur Black 1 solution prepared inExample 1 was added. The test solution of Example 2 was stirred andsparged with air as in Example 1, while maintaining the test solution ofExample 2 at a temperature in the range of 4-6° C. with an ice bath.After 120 minutes a sample of the test solution of Example 2 wascollected, and determined to have a sulfide concentration of less than 5mg/l. This resulted in a reduction of sulfide content by about 98%relative to the initial sulfide concentration of 250 mg/l.

Example 3 C. I. Sulfur Black 1

This test used similar test conditions to Example 2. A test solutioncontaining 250 mg/l sulfide and 250 mg/l of Sulfur Black 1 product washeated to 80° C. at which time air sparging was initiated. After 15minutes of sparging the sulfide concentration had decreased toapproximately 5 mg/l and after 30 minutes, the sulfide concentration haddecreased to less than 1 mg/l, a reduction of over 99.6% relative to theinitial sulfide concentration of 250 mg/l.

Example 4

This test was performed under similar conditions to Example 1 exceptthat the initial sulfide concentration was 100 mg/l and the sulfur dyeproduct concentration was 10 mg/l. After air sparging for 30 minutes ata temperature of 42-45° C., the sulfide concentration had decreased toless than 3 mg/l. This represents a reduction in the sulfideconcentration of about of 97% relative to the initial sulfideconcentration of 100 mg/l.

Example 5 C.I. Sulfur Black 1

This example demonstrates that the dye component can be reused. Aftertreating a test solution of 500 mg/l sulfide and 250 mg/l Sulfur Black 1by air sparging at 50° C. to a final sulfide concentration of less than1 mg/l, the used mixture was replenished with sulfide and re-treated. A1.75 milliliter portion of 5% sulfide was added to 175 milliliters ofused sulfur dye test mixture producing calculated concentrations of 495mg/l sulfide and 247.5 mg/l sulfur black product. This replenishedmixture was stirred and sparged at 50° C. for 105 minutes resulting in afinal sulfide concentration of approximately 6 mg/l, a 98.8% reductionin sulfide concentration relative to the initial sulfide concentrationof 495 mg/l.

Example 6 C.I. Leuco Sulfur Brown 37

This test was similar to previous tests except a sulfur dye productcontaining C.I. Leuco Sulfur Brown 37 was used to treat the sulfidesolution instead of C. I. Sulfur Black 1. A solution of C.I. LeucoSulfur Brown 37 dye was made by diluting 6 grams of DIRESUL Brown RDT-GSliq 150, a liquid dyestuff solution of C.I. Leuco Sulfur Brown 37 dye(Available from Archroma U.S., Inc., Charlotte, N.C.) to 50 milliliterswith distilled water. A 500 mg/l sulfide test solution was prepared bydiluting 50 milliliters of 1000 mg/l stock sulfide solution to 99milliliters. This solution was heated to 45° C. and 1 milliliter of thediluted Brown dye was added to produce a solution containing 1200 mg/lof formulated dye product. The solution was stirred and sparged as inprevious examples. After 30 minutes the sulfide level had dropped byapproximately 90%. After 60 minutes the sulfide concentration was lessthan 20 mg/l, a greater than 96% reduction in sulfide concentrationrelative to the initial sulfide concentration of 500 mg/l.

Example 7 C.I. Leuco Vat Blue 43

This test was similar to previous tests except a dye product containingC.I. Leuco Vat Blue 43 was used to treat the sulfide solution. Asolution of C.I. Leuco Vat Blue 43 dye was made by diluting 12 grams ofDIRESUL Navy RDT-GF 1 liq dyestuff product (Available from ArchromaU.S., Inc., Charlotte, N.C.) to 100 milliliters with distilled water. A500 mg/l sulfide test solution was prepared by diluting 50 millilitersof 1000 mg/1 stock sulfide solution to 99 milliliters. This solution washeated to 45° C. and 1 milliliter of diluted Navy dye was added toproduce a solution containing 1200 mg/l of formulated dye product. Thesolution was stirred and aerated as in previous examples. After 30minutes the sulfide level had dropped by more than 98% to less than 10mg/l. After 60 minutes the sulfide concentration was less than 2.5 mg/l,a greater than 99.5% reduction in sulfide concentration relative to theinitial sulfide concentration of 500 mg/l.

Example 8 C.I. Sulfur Black 1

A test sulfide solution was made by dissolving 3.745 grams of sodiumsulfide nonahydrate in distilled water and diluting to a total volume of99 milliliters. This solution was heated to 45° C. One milliliter of 5%C.I. Sulfur Black 1 solution was then added to produce a test solutionof 5000 mg/l sulfide and 500 mg/l Sulfur Black 1. The test solution wasstirred and sparged with air while maintaining the test solutiontemperature in the 40-45° C. range. After 75 minutes a sample wascollected and determined to have a sulfide concentration of slightlyless than 50 mg/l, a reduction of approximately 99% relative to theinitial sulfide concentration of 5000 mg/l.

What is claimed is:
 1. A method of removing sulfides from wastewatercomprising: removing the wastewater from an anaerobic or facultativetreatment unit to a treatment container; adding at least one sulfur dyeor sulfurized vat dye catalyst to the wastewater to form a mixture;aerating the mixture with a gas comprising oxygen to oxidize thesulfides to yield treated water, wherein the treated water has a reducedconcentration of sulfide relative to the wastewater; and returning thetreated water to the anaerobic or facultative treatment unit, whereinthe sulfides are present in the wastewater as a result of degradation ofbiologically degradable constituents by bacteria during anaerobictreatment.
 2. The method of claim 1, wherein the at least one sulfide isselected from the group consisting of hydrogen sulfide, bisulfide ions,sulfide ions, polysulfide ions and mixtures thereof.
 3. The method ofclaim 1, wherein said sulfur dye is selected from the group consistingof Sulfur Black 1, Leuco Sulfur Black 1, Solubilized Sulfur Black 1, andmixtures thereof.
 4. The method of claim 1, wherein said sulfur dye orsulfurized vat dye is introduced into the wastewater as the Leuco(reduced) form of the dye.
 5. The method of claim 1, wherein thesulfides comprise hydrogen sulfide.
 6. The method of claim 1, whereinthe pH of the mixture is greater than or equal to
 7. 7. The method ofclaim 6, wherein the pH is maintained by adding at least one baseselected from the group consisting of sodium hydroxide, potassiumhydroxide, ammonia, ammonium hydroxide, calcium hydroxide, magnesiumhydroxide, and any combination thereof.
 8. The method of claim 6,wherein the sulfides are converted to a water-soluble salt comprisingthiosulfate ions.
 9. The method of claim 1, wherein the sulfur dye orsulfurized vat dye is separated from the treated water and reused. 10.The method of claim 9, wherein the separation can be effectuated usingfiltration or ultrafiltration.
 11. The method of claim 1, wherein themethod operates continuously or as batch processes.
 12. The method ofclaim 1, wherein the biologically degradable constituents comprise wastefrom animals selected from the group consisting of humans, dairy cattle,beef cattle, swine, poultry, horses, rabbits, and combinations thereof.13. The method of claim 12, wherein the waste comprises at least oneconstituent selected from the group consisting of feces, urine, wastedfeed, bedding drinking water, animal wash water, flush water, andcombinations thereof.
 14. The method of claim 13, wherein the waste ispretreated to remove any unwanted material, larger solids and excessliquids before anaerobic digestion, wherein the pretreating comprises atleast one of a screw press, a centrifuge, a vibrating screen, meshscreening, a belt filter, and a hydrocyclone.
 15. A method forcollecting and treating hydrogen sulfide present as a pollutant inambient air comprising: absorbing said hydrogen sulfide out of theambient air into an aqueous liquid comprising at least one sulfur dye ora sulfurized vat dye to substantially oxidize absorbed sulfides tonon-hazardous constituents.
 16. The method of claim 15 wherein the pH ofthe aqueous liquid is greater than or equal to
 7. 17. The method ofclaim 15 wherein said sulfur dye is selected from the group consistingof Sulfur Black 1, Leuco Sulfur Black 1, Solubilized Sulfur Black 1, andmixtures thereof.
 18. The method of claim 15, wherein the pH of theabsorption liquid is greater than or equal to
 9. 19. The method of claim15, wherein the absorbed sulfides are oxidized by oxygen in the ambientair.